1. Field of the Invention
The present invention relates to electrophotographic image-forming members, used in the field of image formation, which have sensitivity to electromagnetic waves such as light (in a broad sense, infrared rays, visible light, ultraviolet rays, X-rays, .gamma.-rays, and the like).
2. Description of the Prior Art
Se, Si-Te, CdS, ZnO, and organic photoconductive materials such as PVCz, TNF, and the like are well-known as a photoconductive material constituting a photoconductive layer in an electrophotographic image-forming member. Meanwhile, amorphous silicon (hereinafter, represented by a-Si) has recently attracted attention as a hopeful photoconductive material, as disclosed in, for example, Ger. Pat. Offen Nos. 2746967 and 2855718, in its characteristics comparable to other photoconductive materials in photosensitivity, spectral wave region, response to light, dark resistance, etc.; additionally ease of p-n control despite its amorphous nature, and harmlessness to the human body during usage.
As mentioned above, a-Si has many superior characteristics to other photoconductive materials, and its practical application to electrophotographic image-forming members is speedily pushed forward; however, there still remain some points to be solved.
For instance, the conventional electrophotographic image-forming member having a photoconductive layer of a-Si requires further improvements in electrical, optical, and photoconductive characteristics such as dark resistance, photosensitivity, response to light, and the like, in working environment resistance such as moisture resistance, and also in stability for time passage. In order to apply a-Si to electrophotographic image-forming members practically useful over a wide range of applications, improvements in productivity and mass productivity are also necessary.
In some cases, for instance, residual potential is observed during survice operations. Repeated usage for many hours results in fatigue accumulation, thereby causing objectionable things such as a ghost phenomenon, whitening in transferred images, and the like.
Moreover, when the layer thickness becomes ten and several microns or more, the layer tends to cause a phenomenon such as floating (partial separating) or peeling from the substrate surface or formation of crack in itself with the elapse of standing time in the air after taking out from a vacuum-deposition chamber for layer formation. These phenomena tend to occur particularly in the case of a cylindrical substrate, which is commonly used in the field of electrography. Such being the case, there are points to be solved in respect to stability for time passage.
In view of the above, this invention has been accomplished as a result of extensive and intensive studies on photoconductive layers of amorphous materials containing silicon atoms as matrix, hydrogen atoms (H) and/or halogen atoms (X) [hereinafter, these amorphous materials are represented by a-Si(H,X)], in particular studies of characteristics of said layers themselves and studies of relations between said layers and substrates on which said layers are laid, from the standpoints of mechanical, electrical, photo-conductive, and durable characteristics.
The present inventors observed that it is necessary; to increase the dark resistance of a-Si(H, X) while keeping its inherent high photosensitivity; to eliminate or relax the large strain generated in the layer during layer formation, to a non-influential level by some means, since said strain causes such floating or peeling from the substrate or layer cracking; to optimize the mechanical or electrical contact between the substrate and the a-Si(H,X) layer and improve closeness between them; to establish such optimum conditions as to satisfy the above-mentioned requirements at the same time, in order to obtain an electrophotographic image-forming member excellent in electrophotographic performance characteristics, particularly in working durability. Based on these observations, the present inventors further continued extensive researches and examinations and were successful in establishing such optimum conditions.